1. Field of the Invention
The present invention relates to a small power pack primarily intended for reducing an incoming line voltage of either 110 or 220 volts to provide a low voltage alternating current supply. With rectification, the pack may provide a selected low voltage direct current supply, a low voltage battery charger supply, or a choice of A.C. or D.C. supply voltages. The device is generally useful for small electrically-powered devices such as cordless grass shears, shrub trimmers, calculators, electric razors, and the like. The invention is more specifically related to the switch and multi-tap winding configurations employed in the pack.
2. Description of the Prior Art
The use of power packs is becoming more popular for small appliances where it is desired to operate the appliance at a voltage substantially lower than the 110/220 volt line voltage or to operate by battery. Power packs for small appliances, e.g., calculators, are presently being marketed where the 110 volt A.C. line voltage is reduced to 12 volts and can be rectified to provide D.C. voltage (see U.S. Pat. No. 3,711,806). Another example of power pack usage is where nickel cadmium batteries are employed for powering small appliances, e.g., portable grass and hedge shears, and a need to recharge the batteries from time to time requires the use of a reduced voltage operated battery charger power pack. The reduction of voltage to a lower level, e.g., below 30 volts R.M.S., by use of a power pack is significant to assist in obtaining Underwriters' Laboratories approval on appliances and other world agency approvals.
While domestically made power packs which are adapted for 110/220 volt incoming supply are available, their cost is too high. The main reasons of high cost reside in labor costs caused by excessive taping, staking, gluing and potting operations and by the nature of the switching devices necessitated to provide a power pack unit that will operate on 110 or 220 volts A.C. and will meet Underwriters' Laboratories approval. The switches used to switch from 110 to 220 volt supply or vice versa have been conventionally mounted on the casing or cover and have not been incorporated in the bobbin structure.
U.S. Pat. Nos. 3,711,806; 3,371,302 and 3,237,079 are illustrative of patents which are related to power pack construction and which illustrate related prior art devices and practices.